Comparison of rates of surface-elevation change on the Greenland ice sheet
derived from European Remote-sensing Satellite-2 (ERS-2) radar-altimeter
data with those obtained from laser-altimeter data collected over
nearly the same time periods.

Global SST fields were created using a variety of techniques including Reduced Space Optimal Interpolation (RSOI). Sea ice concentration fields from different sources were analysed to make them as consistent as possible through time. Some care should be taken when using the sea-ice concentration data, particularly in the Southern Hemisphere where there is no realistic interannual variability in sea ice prior to 1973. The HadISST1 data set has been shown to be an improvement upon (and has superseded) the GISST data set.

PERMOS is based on three types of observations: (1) ground temperatures measured at and below the surface at borehole sites, (2) changes in subsurface ice and unfrozen water content at these sites in- ferred by geoelectrical surveys, and (3) velocities of permafrost creep determined by geodetic surveys and/or photogrammetry. In addition, standardized documentation of fast mass movements from permafrost areas (e.g., rock fall) is being established.

The Sea Ice Index provides a quick look at sea ice changes in spatial and
historical context and gives a consistent, up-to-date source of sea ice extent
and sea ice concentration values and images. The NSIDC Near-Real-Time DMSP SSM/I
Daily Polar Gridded Sea Ice Concentrations and the Sea Ice Concentrations from
Nimbus-7 SSMR and DMSP SSM/I Passive Microwave Data data sets are used to
generate the monthly records of sea ice extent and sea ice concentration for the
Arctic and Antarctica from satellite passive microwave data.
Data files tabulate monthly mean extent and area, in millions of square
kilometers, by year for a given month. Plots of monthly sea ice extent anomalies
with trend lines and significance intervals are available. Monthly images show
sea ice extent (with an outline of the median extent for that month for
comparison), sea ice concentration, trends in sea ice concentration, and
anomalies in sea ice concentration. Anomalies and median extent are calculated
using a reference period of 1979 through 2000.

A comparison of monthly anomalies in Northern Hemisphere SCA derived from two satellite data sets: the NOAA snow charts revised by D. Robinson that map snow cover from primarily visible-wavelength sensors like AVHRR and GOES, and passive microwave (PM) algorithms using SMMR and SSM/I EASE-Grid brightness temperatures. Since both data sets exhibit significant month-to-month autocorrelation, we have estimated monthly trends with an autoregressive lag-1 model (AR(1)), using the method described by Weatherhead et al. (1998).